Transport device with slave control

ABSTRACT

A transport device including a driving part with at least one driving device for moving the driving part in a number of directions on a surface. Also present is a carrying part which is arranged above the driving part and intended to carry a load. The driving part and the carrying part are movable in relation to one another in a number of directions essentially parallel to the surface. A measuring device is arranged for measuring a positional difference between the driving part and the carrying part. The driving device is adapted to drive in directions which depend on the positional difference between the driving part and the carrying part. In this way, a transport device of which the movement can be controlled in a natural and exact way is produced.

TECHNICAL FIELD

The present invention relates generally to a device for the transport ofmaterials and more specifically to a device in which a wheeled carrieris made to follow a course by using slave control.

BACKGROUND

When materials are moved by means of, for example, a vehicle orconveyor, it is sometimes an advantage to bring about the movement byapplying a force to the vehicle or the component instead of controllingit by means of a control mechanism. Examples of such applications arethe transport and positioning of materials for a moving assembly line.When components are positioned, it is an advantage for it to be possibleto guide the component into position by applying a force to it. With theproposed solution, the component automatically follows the movements ofthe assembly line during and after mounting thereof.

In the handling described above, use is today made of, for example,air-cushion-supported conveyors. These can be moved with unlimitedmobility but they have no servo function, which leads to great strainduring starting and deceleration when great masses are transported.

SUMMARY OF THE INVENTION

One object of the invention is to produce a device which makes itpossible to apply only a small force in the desired transport direction,which leads to a servo function being activated, the servo action beingreversed and changing over to decelerating the mass of the vehicle whenthe force applied ceases.

The invention is based on the insight that a transport device can bearranged with a driving part and a carrying part which are movable inrelation to one another, sensors which measure the relative position ofthe parts making possible a slave-control function for driving thetransport device in the desired direction.

According to the invention, a transport device as defined in Claim 1 istherefore produced.

Further preferred embodiments are defined by the subclaims.

The abovementioned problems of the prior art are solved by the transportdevice according to the invention. By virtue of the fact that arelatively small force which is applied to the carrying part can beregistered, which leads to the driving means of the carrying partdriving in the desired direction, a device of which the movement can becontrolled in an exact way is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail as an example, withreference to accompanying drawings, in which:

FIG. 1 a shows a side view of a transport device according to theinvention;

FIG. 1 b shows a top view of the transport device shown in FIG. 1 a;

FIG. 1 c shows a transparent perspective view of the transport deviceshown in FIG. 1 a;

FIG. 1 d shows a simplified block diagram of the parts which make up thedriving system for the transport device according to the invention;

FIGS. 2 a-c show views corresponding to those shown in FIGS. 1 a-c butwhen a force is applied to the carrying part of the transport device ina longitudinal direction;

FIGS. 3 a-c show views corresponding to those shown in FIGS. 1 a-c butwhen a force is applied to the carrying part of the transport device ina transverse direction;

FIGS. 4 a-c show views corresponding to those shown in FIGS. 1 a-c butwhen a force is applied to the carrying part of the transport device ina diagonal direction;

FIGS. 5 a-c show views corresponding to those shown in FIGS. 1 a-c butwhen a force is applied to the carrying part of the transport devicewhich results in a turning movement of the transport device;

FIGS. 6 a-c show views corresponding to those shown in FIGS. 1 a-c butwhen a force is applied to the carrying part of the transport devicewhich results in a rotation of the transport device;

FIG. 7 a shows an overall view of the transport device according to theinvention in an alternative embodiment;

FIG. 7 b shows a detailed view of the link between the transport deviceshown in FIG. 7 a and an aircraft, and

FIG. 7 c is a view similar to that in FIG. 7 b but showing analternative embodiment of the transport device according to theinvention.

EMBODIMENTS

Preferred embodiments of a transport device according to the inventionwill be described below. In the description, for the purpose ofclarification but not limitation, specific details will be shown inorder to afford a thorough understanding of the present invention. Theexpert will nevertheless understand that the invention can be used inother embodiments which differ from these specific details. Specificdirections, such as up, down, left, right etc., are also indicated inthe description. It is to be understood that these directions only referto what is shown in the figures and are therefore not limiting as far asthe practical applications of the invention are concerned.

Reference is initially made to FIGS. 1 a-c. FIG. 1 a shows a simplifiedside view of a transport device, designated generally by 10, which is inthe rest position, that is to say no external force is applied to it.The transport device comprises a driving part 20 and, arranged above thedriving part, a carrying or fixture part 30. The two parts 20, 30 areinterconnected with sensors, one 40 a of which is shown in FIG. 1 a. Inthe preferred embodiment, the sensors are in the form of strain gauges.

The driving part is adapted to be driven on a surface by using fourwheels 22 a-d (see FIG. 1 b). The wheels are preferably of the typewhich is described in international patent publication WO99/54190, whichis included herein by reference. Therefore, two diagonally oppositewheels 22 a, 22 c are driving wheels which can be swivelled into thedesired position while the two other wheels 22 b, 22 d are swivellingbut not driving wheels. By virtue of this, the driving part can drive inessentially any direction parallel to the surface.

The driving and carrying parts are separated from one another by adividing plane 18 consisting of an interspace, the size of which hasbeen exaggerated in the figures for the sake of clarity. The dividingplane is essentially parallel to the surface on which the vehicle isintended to run, and the connection between the driving part and thecarrying part can be brought about in various ways. Common to these isthat the levels can move in relation to one another in directions whichare parallel to the surface on which the transport device is moved, and,in the preferred embodiment, the carrying part rests on rubber blockswhich are arranged on the driving part. This allows small, but readilydetectable relative movements between the driving part and the carryingpart, which are used for the desired servo function.

FIG. 1 d shows the parts which make up the driving system. The drivingwheels 22 a, 22 c are driven by respective driving arrangements 24 a, 24c consisting of an electric motor with associated mechanics andelectronics. The driving arrangements are connected to a central unit 26consisting of a microprocessor and associated electronics. The sensors40 a, 40 b are also connected to this central unit. Finally, there is adisplay/input unit 28 which is connected to the central unit and servesas a user interface.

When a force is applied to the carrying part in any direction, arelative movement between the driving and carrying parts occurs, asmentioned, which results in a positional difference between them. FIGS.2 a-c show the effect of a force being applied to the carrying parttowards the left, as can be seen from the arrows. The carrying part isimparted a movement which instantaneously results in a positionaldifference Δx in the longitudinal direction of the transport device.This positional difference is detected by means of the sensors 40 a, 40b, and information about this is sent to the central unit which uses thepositional information as a basis for driving commands which are sent tothe driving arrangements 24 a, 24 c. In the example shown in FIGS. 2a-c, the wheels therefore start to drive towards the left in the figure.

When the wheels start to drive, the driving part 20 strives to take upthe same position as the carrying part 30, that is to say to reduce Δx.If the force which is applied to the carrying part is static, whichmeans, for example, that the user who pushes the carrying part does notmove, the driving part will move until Δx is zero while the absoluteposition of the carrying part does not change. When Δx is zero, thedriving wheels cease driving, and the transport device has been moved toa new position.

If, on the other hand, the force which is applied to the carrying partis dynamic, that is to say the user who pushes the carrying part movesin the same direction as the force, Δx remains greater than zero as longas the user moves. Only when the driving part is allowed to “catch upwith” the carrying part does the driving cease.

As mentioned previously, the positional difference between the drivingpart and the carrying part is used as a parameter for the commands whichthe central unit sends to the driving arrangements. This means that thegreater the force applied, the greater Δx is. A greater value of Δxmeans higher driving speed, as a result of which the transport devicemoves at different speeds depending on how hard the user pushes thecarrying part. When pushing ceases, the transport device stopsessentially instantaneously.

In other words, the driving part and the carrying part are made, via forexample spring-loading, to strive towards a neutral point at which theservo action ceases, and, as soon as the applied force ceases, the servoaction changes over from driving aid to deceleration aid.

The movement direction does not have to be limited to that shown inFIGS. 2 a-c. FIGS. 3 a-c show the effect of a force being applied to thecarrying part in the transverse direction of the transport device. Thisresults in a positional difference Δy which in turn brings about amovement transverse to the longitudinal direction of the transportdevice.

A combination of these movements is of course possible. FIGS. 4 a-c showthe situation when the resulting force is directed diagonally, that isto say consists of a component in both the longitudinal direction andthe transverse direction. The sensors 40 a, 40 b register the relativepositional differences, Δx and Δy, and the central unit 26 uses thisinformation in order to bring about driving in the diagonal direction.

In the driving examples described above, the two sensors 40 a, 40 bdetected the same relative positional difference, that is to say therelative movement between the driving part and the carrying partconsisted exclusively of a translational movement, which has notresulted in any turns, that is to say any rotational movement. FIGS. 5a-c show an example of when the transport device turns. FIG. 5 b showshow a smaller force is applied to the lower part of the carrying partthan the upper part. This results in the lower sensor 40 a registering asmaller positional difference than the upper sensor 40 b. Thispositional information results in the central unit ordering the upper,right wheel to drive in one direction and the lower, left wheel 22 c inanother direction. The combined result is a turning movement as shown bythe arrow on the left in FIG. 5 b.

A pure rotational movement can also be brought about, as can be seenfrom the example shown in FIGS. 6 a-c. FIG. 6 b shows how a forcedirected towards the left is applied to the lower part of the carryingpart while a force of the same magnitude directed towards the right isapplied to the upper part. This results in the two driving wheelsdriving in opposite directions, which brings about a pure rotationalmovement.

It may be an advantage to make the transport device drive more easily inone direction than another, which can be brought about simply with thetransport device according to the invention. Such programming ofcharacteristics can be brought about by means of the input unit 28. Anexample of such programming may be that a relative positional differencein the transverse direction, that is to say Δy, is made to have lessinfluence on the driving than a relative positional difference in thelongitudinal direction, that is to say Δx. This can also be broughtabout purely mechanically by virtue of the applied force necessary tobring about a relative positional difference being different indifferent directions. However, the basic principle of the system is theservo action in all directions and also possible rotation about a centreor one or more other selected point(s).

The proposed solution affords a number of advantages, the most importantof which are described below. The transport device according to theinvention affords the possibility of moving large masses in the mostlogical way—applying a force directly to the mass, the servo actionmoving the mass in this direction as long as the force is applied. Thepossibility of using wheel-mounted conveyors for materials for movingassembly lines is also afforded. Movement can be effected with verygreat precision compared with current corresponding solutions of theair-cushion type.

A preferred embodiment of a transport device according to the inventionhas been described. The expert in the technical field concerned willunderstand that this can be varied within the scope of the accompanyingpatent claims. It has been mentioned that the driving and carrying partsare preferably connected by means of rubber blocks, to which othercomponents with corresponding elastic properties are equivalent.Alternatively, slide rails can be arranged in, for example, thelongitudinal direction and the transverse direction, the parts beingreturned to the same relative position by means of, for example,springs.

The sensors 40 a, 40 b have been described as strain gauges. Alternativesensors are of course also possible, such as optical sensors ormechanical sensors which function as a joystick. The positioning andnumber of the sensors can also be varied as required, for example inorder to detect more complex movements.

The driving in the preferred embodiment is effected by wheels. Othertypes of driving means are of course also possible, such as drivingbelts. The positioning and number of the driving means can also bevaried as required. Therefore, for example, one driving wheel can becombined with two or more non-driving wheels, three or more drivingwheels can be combined with an appropriate number of non-driving wheels,or there can be no non-driving wheels. In the case of two drivingwheels, they can be positioned diagonally, as in the embodimentdescribed, or they can be positioned along the same side. As a furtheralternative, one or more wheel(s) can be supplemented by an air-cushionarrangement.

FIG. 7 a shows an alternative embodiment of a transport device 100,which is slaved to another object, shown in the figure as an aircraft120. In this case, the positional difference measured is that between atransport device 100 in the form of a working platform and the aircraft120. This is brought about by means of two sensors 140 a, b which arearranged on one side of the transport device (see FIG. 7 b). These canbe, for example, laser sensors which work against respective reflectivesurfaces 142 a, b on the aircraft body. In this way, it is possible tokeep track of the relative distance Δx1, Δx2 between the aircraft andthe transport device.

In this case, the slave control takes place in the following way. In adesired relative position of transport device and aircraft, the sensorsand control system are zeroed. This position therefore corresponds tothat shown in FIGS. 1 a-c for the first embodiment. If the aircraftbegins to move from this position, this will be detected by the sensors140 a, b. The deviation from the relative positional difference in thestarting position serves as an input signal for the control system ofthe transport device, which, in the same way as in the first embodiment,tries to drive the transport in a direction which returns it to thestarting position relative to the plane. In this case, the transportdevice is slaved to the other object, shown as an aircraft.

It will be understood that measurement can be carried out in ways otherthan that shown in the figures. For example, it is possible to have atelescoping arrangement which is arranged between the aircraft and thetransport device and with which the relative distance between them ismeasured. Furthermore, in addition to or instead of pure distancemeasurement, it is also possible to use angular measurement, that is tosay how the aircraft has moved relative to the transport device ismeasured in another dimension. FIG. 7 c indicates two angles α and β,and a relative positional difference can be calculated by means of theseangles.

In the embodiment which has been described with reference to FIGS. 7a-c, an aircraft has been used as an example of the object of which thetransport device follows the movement. This is of course only anexample, and an alternative is, for example, a car on a production line.

1. A transport device comprising: a driving part with at least onedriving means for moving said driving part in a number of directions ona surface, a carrying part arranged above said driving part and adaptedto carry a load, wherein said driving part and said carrying part aremovable in relation to one another in a number of directions essentiallyparallel to said surface, said transport device comprising a measuringmeans for measuring a positional difference between said driving partand said carrying part, and said driving means being adapted to drive indirections which depend on said positional difference between saiddriving part and said carrying part.
 2. The transport device accordingto claim 1, in which said driving means comprises at least one wheel. 3.The transport device according to claim 1, in which said driving meanscomprises at least one driving belt.
 4. The transport device accordingto claim 1, in which said measuring means comprises strain gauges. 5.The transport device according to claim 1, in which said measuring meanscomprises optical sensors.
 6. The transport device according to claim 1,in which said measuring means comprises a joystick arrangement.
 7. Thetransport device according to claim 1, comprising elastic spacers,preferably rubber blocks, arranged between said driving part and saidcarrying part.
 8. The transport device according to claim 1, comprisingslide rails arranged between said driving part and said carrying part.9. The transport device according to claim 1, in which said drivingmeans are adapted to drive at a speed which is essentially proportionalto said positional difference.
 10. The transport device according toclaim 1, in which said driving means are adapted to drive at a greaterspeed in a first direction than in a second direction for the samepositional difference.